1. Field of the Invention
This invention relates to an image display device for forming a visible image for display on a recording medium.
2. Description of the Related Art
Various kinds of devices for forming a visible image for display in accordance with image information have been developed. One such device uses conductive magnetic toner which serves as a fine-particle developer. The toner is electrostatically applied onto a recording medium, and the resultant image is displayed.
A method has, for example, been proposed in Japanese Patent Application No. 49-44336 (1974) (corresponding to U.S. Pat. No. 3,816,840). According to this method, as shown in FIG. 10, conductive magnetic toner 51 adhered to the outer circumference of a nonmagnetic cylinder 50 is moved by a magnetic field generated by a rotating magnet 52 provided coaxially with the nonmagnetic cylinder 50. The toner 51 is passed through recording electrodes 50a which are densely arranged along the direction of the axis on the outer circumferential surface of the nonmagnetic cylinder 50. When the toner 51 physically contacts a recording medium 53, which comprises an insulating layer 53a laminated on a conductive layer (cylinder) 53b provided close to the non-magnetic cylinder 50, voltage is applied to the recording electrodes 50a from a power supply unit 54. By applying a voltage between the recording electrodes 50a and the conductive layer 53b of the recording medium 53 in accordance with image information and thereby injecting electric charges from the recording electrodes 50a into particles of the toner 51, the particles of the toner 51 electrostatically adhere to the insulating layer 53a of the recording medium 53, thus forming an image.
In an image forming device for display to which the above-described image forming method is applied, as shown in FIG. 11, the toner 51 is moved to the recording electrodes 50a by rotation of a magnetic roller (not shown), and particles of the toner 51 adhere or do not adhere to the recording medium 53, which is moved by a driving moving roller 55a and a driven moving roller 55b, in accordance with signal voltages from the recording electrodes 50a, thus forming an image.
The driving moving roller 55a is driven by a driving motor 56 whose speed is controlled by a control unit 58 via a motor driver 57. An encoder 59 detects the moving speed of the recording medium 53. A page memory 60 stores image information.
FIG. 12 is a timing chart corresponding to a control sequence performed by the control unit 58. Symbol "a" represents a motor control signal. In a motor speed control signal b, a high level corresponds to the moving speed of the recording medium to perform recording, and a low level corresponds to a reduced moving speed. Symbol c represents an output waveform of the encoder 59, and symbol d represents memory read pulses to be input to the page memory 60.
FIG. 13 is a timing chart when image data are output from the page memory 60 to the recording electrodes 50a.
When a memory read pulse e has been input to the page memory 60, a data enable signal f for requesting the output of image data, a clock signal g for transmitting image data for one line, image data h, and a strobed pulse i for applying the image data h to the recording electrodes 50a are output.
That is, by outputting the strobe pulse i to the recording electrodes 50a with a constant period while moving the recording medium 53 at a constant speed, an image can be formed on the recording medium 53 for every line with a constant interval.
However, in the above-described configuration, as shown in the timing charts of FIGS. 12 and 13, an image forming operation is started by inputting the memory read pulse e to the page memory 60 after the moving speed of the recording medium 53 has become constant. Accordingly, as shown in FIGS. 14(a) and 14(b), an image forming area is smaller than a display area of the recording medium 53, thus decreasing the efficiency of the use of the display area.
As shown in FIG. 14(a), the recording medium 53 may have connecting portions 53c of recording media on which a recording image cannot be formed. In such a case, the most efficient use of the image forming area can be realized by aligning the connecting portion 53c to face the recording electrodes 50a and starting recording from that position. However, even if such approach is taken, it is impossible to prevent the image forming area from being narrow. The same problem is present even in a recording medium not having areas on which an image cannot be recorded as described above, and in a recording medium which has a predetermined specific position to start recording or stop the recording medium.